Hi,For this test you will need a multi meter, set it to 12volt D.C. and attach probes Red to Positive + on battery Black to Negative - on battery then start the car, the reading should show anywhere between 13.8 to 14.9 volts, if it stays around 12.5ish then the alternator isn't working.One other way to get an idea is to put all headlights on from tickover with engine running rev up if they go brighter your alternator is working but still might not be putting enough in the system.Press the Blue Button please to appraise my FREE! Effort.Thank You!Paul 'W' U.K.

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check battery terminals and posts are shiny clean and tight. Have a load test done on the battery to test for failing cell. Have alternator checked for out put and check alternator drive belt for condition and tension

Locate the two belts on the left
side (passenger side) of your Mitsubishi Lancer. The outer belt is a
serpentine belt, operating four pulleys and the inner belt is your
alternator belt.

2
Follow the serpentine (outer)
belt to the three pulleys lined up vertically near the front of the
engine compartment. Locate the middle pulley, which is the tension
pulley for the belt.

3
Loosen the bolt on the middle
pulley with a socket wrench by turning counter-clockwise. Do not remove
the bolt, just turn it a couple of times. Loosen the tensioner bolt on
the side of the of the pulley, facing the front of the vehicle.

4
Remove the serpentine belt and
then loosen the bolt on the alternator. With the alternator loose, move
it forward so that the alternator belt loosens up and then remove belt
from the pulleys.

5
Install the new alternator belt
by placing it over both inside pulleys. Tighten the tension on the
alternator belt by moving the alternator back and keeping tension on it
by holding it back with a long screwdriver. While the alternator belt is
tight, use a socket wrench to tighten up the bolt on the alternator.

6
Place the serpentine belt back
on the pulleys and then use a socket wrench on the bolt on the front of
the tension pulley. Once the serpentine belt is tight, tighten up the
bolt in the middle of the tension pulley.

7
Start the Mitsubishi Lancer's
engine to test the alternator belt and make sure it is working properly.
Once you have verified it is working, turn the engine off.

Locate the two belts on the left side (passenger side) of your Mitsubishi Lancer. The outer belt is a serpentine belt, operating four pulleys and the inner belt is your alternator belt.

2

Follow the serpentine (outer) belt to the three pulleys lined up vertically near the front of the engine compartment. Locate the middle pulley, which is the tension pulley for the belt.

3

Loosen the bolt on the middle pulley with a socket wrench by turning counter-clockwise. Do not remove the bolt, just turn it a couple of times. Loosen the tensioner bolt on the side of the of the pulley, facing the front of the vehicle.

4

Remove the serpentine belt and then loosen the bolt on the alternator. With the alternator loose, move it forward so that the alternator belt loosens up and then remove belt from the pulleys.

5

Install the new alternator belt by placing it over both inside pulleys. Tighten the tension on the alternator belt by moving the alternator back and keeping tension on it by holding it back with a long screwdriver. While the alternator belt is tight, use a socket wrench to tighten up the bolt on the alternator.

6

Place the serpentine belt back on the pulleys and then use a socket wrench on the bolt on the front of the tension pulley. Once the serpentine belt is tight, tighten up the bolt in the middle of the tension pulley.

7

Start the Mitsubishi Lancer's engine to test the alternator belt and make sure it is working properly. Once you have verified it is working, turn the engine off.

You have what's known as a "Parasitic Battery Drain". This is a condition where voltage leaves the battery when the vehicle is off and the key is out of the ignition. The test and solution is too long to post here."Google Parasitic Battery Drain" and you'll find countless sites that offer the test and solution.